Simplify the following expression: $k = \dfrac{15z + 5}{10z - 20x} + \dfrac{25z}{10z - 20x}$ You can assume $x,y,z \neq 0$.
Answer: Since the expressions have the same denominator we simply combine the numerators: $k = \dfrac{15z + 5 + 25z}{10z - 20x}$ $k = \dfrac{40z + 5}{10z - 20x}$ The numerator and denominator have a common factor of $5$, so we can simplify $k = \dfrac{8z + 1}{2z - 4x}$